MAYOR— DETECTING OCEAN CURRENTS. 159 



west is decidedly alkaline, about 8.23 PH, and its carbon dioxide 

 tension is about 0.0003 atmospheres, and thus about in balance with 

 the air. Back set currents moving in an easterly direction are, how- 

 ever, often encountered in the equatorial mid-Pacific especially in 

 about 5° north latitude. This water is somewhat cooler than that 

 of the prevailing westerly current, its carbon dioxide tension is de- 

 cidedly acid, ranging from about 8.1 to 8.18 PH. Thus it comes 

 from depths wherein the w'ater is at least from 5° to 13° C. colder 

 than the temperature of the surface of the ocean, and therefore from 

 at least 100 to 200 fathoms beneath the surface (see chart No. 19, 

 " Narrative of Challenger Expedition," Vol. i, part 2, p. 758). 



The gusty character of the trade winds combined with the gen- 

 eral up-welling of deep water in the equatorial region may be a 

 primary cause of this easterly current which consists of deep water 

 that has come to the surface. 



My conclusions support those of McClendon that the PH of sea 

 water is dependent chiefly upon the temperature, and not upon the 

 salinity of the water. A fall of 1° C. in temperature normally cor- 

 responds with a decline of about 0.0 1 in the PH as found by Mc- 

 Clendon, but this may be altered by local conditions, such as dilution 

 by relatively acid fresh water, or by the coming to the surface of 

 cool deep water heavily charged with COo which it discharges into 

 the atmosphere upon being heated. 



The cold shore current along the Atlantic coast of America be- 

 tween Nova Scotia and Florida is relatively acid in comparison with 

 the Gulf Stream, being 7.9 to about 8.1 in winter, and its carbon 

 dioxide tension is lower than that of the air, due possibly to photo- 

 synthesis maintained by its abundant plant life. It is thus absorb= 

 ing carbon dioxide from the air. Thus the colder surface waters 

 are absorbing carbon dioxide, while the tropical regions are probably 

 setting it free into the atmosphere. 



The detection of the sudden and marked change from blue-green 

 to yellow-green when one encounters an easterly set in the Tropical 

 Pacific, or passes from a warm into a cold current, can be so easily 

 made that this method may prove of value in navigation. 



